This invention relates to the testing of bond strength of materials and more particularly to methods and apparatus for measuring and testing the strength of a bond between an element or a coating and a surface, body, or substrate to which the element or coating has been attached. In the case of a coating for example, this might be a protective coating, such as paint or metal cladding on an element which in use would be subject to corrosive environments, or simply oxidation. Another example would be metal cladding on a nuclear fuel element,
Adhesion testers of the type of this invention for testing the bond strength of materials are shown and referred to in U.S. Pat. No. 4,567,758, to R. K. Fisher and & L. Fisher, the teachings of which are incorporated in their entireties herein by reference. This prior patent points out that although adhesion testers of this type have been made in various forms which operate in different ways they generally have four steps in common: (1) attaching a fastener to the material to be tested, (2) applying a tensile force to the fastener along an axis normal to the surface, (3) measuring the maximum tensile force required to cause bond failure, and (4) computing a relative measure of the bond strength by dividing the maximum tensile force by the area of the stressed surface of the failed bond. The Fisher patent then discusses major problems encountered in each of these steps and the manner in which these problems are overcome by the apparatus invention set forth in said patent.
However, there is an additional problem in carrying out step (1) in that an undesirable amount of time is necessary for curing of the adhesive such as epoxy or other suitable material, which is strong enough for the intended purpose for example, used to attach the fastener to the coating or layer to be tested. This delays the measuring and testing process and can be costly, particularly in a continuously operating system, such as in a production or assembly line, or where rigid time constraints are required to meet a predetermined schedule, for example.
Additional prior patents in the field of testing of bond strength of materials are discussed below. U.S. Pat. No. 4,586,371 shows an apparatus for testing the adhesive bond strength between a coating and a substrate using a piston and cylinder coupled to a dolley which is adhesively connected to the coating by cured epoxy. U.S. Pat. No. 5,176,028 shows an apparatus and method for testing bond strength of overlapped ends of substrate material to which adhesive has been applied to bond the ends together. The ends are pressed together with the bonding material between them by opposing press heads having heaters for heating the test samples during pressing for a predetermined time interval to assist in setting the bond material. The ends are then sheared apart and data is compiled representing the relationship between bonding strength development and temperatures, and between bond strength and bonding pressure. U.S. Pat. No. 5,671,634 shows an apparatus and method for testing adhesion quality of coatings applied onto a substrate wherein a pulling element has a face at one end which is joined to the coating by an adhesive disk preferably made of cyanoacrylate having a thermosetting temperature of about 25 C and a curing time of 15-30 minutes. A piston and cylinder device connected to the pulling element operates to pull the latter and the disk in a direction normal to the coating tending to separate the coating from the substrate. Prior to the pulling operation the assembly is subjected to heat to set the adhesive disk.
It is also known to use light curable adhesives for securing various elements together, such as a cyanoacrylate material known as "Loctite"4304.
These prior art patents all have the same time delay problems pointed out above in that considerable time may be lost in carrying out the process due to the curing time required for the adhesive. The present invention provides a solution to these problems.
It is also known to use high intensity light devices for various purposes, such as described in U.S. Pat. No. 4,729,070, powered by a compatible lamp source to provide the desirable light intensity.